Several techniques, systems, and supporting structures have been developed for correcting and stabilizing the spine. Some systems use supporting structures like a rod, a tether, a ligament, or others disposed longitudinally along a length of the spine or vertebral column. In accordance with such a system, the supporting structure is engaged to various vertebrae along a length of the spinal column by way of a number of fixation elements. A variety of fixation elements are configured to engage specific portions of the vertebra. For instance, one such fixation element is a hook that is configured to engage the laminae of the vertebra. Another very prevalent fixation element is a spinal bone screw which can be threaded into various aspects of the vertebral bone or pelvis. For example, a plurality of spinal bone screws can be threaded into a portion of several vertebral bodies and the sacrum, such as, for example, the pedicles of these vertebrae. The supporting structures can then be affixed to these spinal bone screws to apply corrective and stabilizing forces to the spine.
Because conventional rods and screw are rigid, relatively high levels of stresses and strain can be introduced to the supporting bone structure during cyclic loading that occurs during a patient's normal activities. Conventional fixation elements can be improved to more easily accommodate the loads, while reducing the introduction of stress into the boney support tissue.
The devices and systems disclosed herein overcome one or more of the shortcomings of prior art devices.